Problem 162 - A Complete Resource Book in Chemistry for JEE Main

Question

What happens when a lyophilic sol is added to a lyophobic sol? (a) Lyophilic sol is protected (b) Film of lyophobic sol is formed over lyophilic sol (c) Lyophobic sol is protected (d) Film of lyophltic sol is formed over lyophobic sol.

Step-by-Step Solution

Answer

(c) Lyophobic sol is protected.

Step 1: Understanding the Concepts

Lyophilic sols are colloidal suspensions where the dispersed phase has an affinity for the dispersion medium, making them stable and reversible. Lyophobic sols, on the other hand, do not have an affinity for the dispersion medium and are less stable.

Step 2: Examining the Interaction

When a lyophilic sol is added to a lyophobic sol, the lyophilic sol can surround the particles of the lyophobic sol. This stabilization prevents the lyophobic particles from coagulating, which is why lyophobic sols are considered protected.

Step 3: Identifying the Correct Option

Given the role of lyophilic sols in stabilizing lyophobic sols, the most suitable answer from the provided options is that the lyophobic sol is protected by the presence of a lyophilic sol.

Key Concepts

Lyophilic sol

Lyophilic sols, also known as hydrophilic sols, are a type of colloidal system where the colloidal particles have a strong affinity for the dispersion medium. This means that the particles can mix well with the medium, making the sol quite stable. These are typically formed when substances such as gelatin, starch, or proteins dissolve in water.

Lyophilic sols are characterized by several important properties:

• Stability: Due to their natural affinity to the solvent, lyophilic sols do not easily precipitate or coagulate. They remain in a stable and reversible state. If water evaporates, these sols can regain their state just by adding the solvent back.


• Viscosity: These sols often exhibit higher viscosity compared to their respective dispersing solutions.


• Tyndall Effect: They may or may not show the Tyndall effect as light scattering depends on the nature of the sol.

Overall, lyophilic sols play an important role in the stability of other colloids by preventing their coagulation, as we will see with lyophobic sols.

Lyophobic sol

Lyophobic sols are a kind of colloidal solution where the dispersed phase and the dispersion medium do not mix well, resulting in a lack of natural affinity between them. Because of this, lyophobic sols require stabilization agents to avoid coagulation.

These are typically inorganic substances such as metals and sulphides and require specific preparation methods like condensation or dispersion to create.

Here are some key characteristics of lyophobic sols:

• Lower Stability: Without any stabilization, these sols are prone to coagulation. They generally rely on external stabilizing agents such as electrolytes or lyophilic sols for stabilization.
• Irreversibility: Once coagulated, lyophobic sols cannot simply be reformed by adding the dispersion medium back.
• Highly Sensitive: These sols are sensitive to temperature changes and electrolytes in the solution.

Understanding the stabilization of these sols is critical. When lyophilic sols are added, they help by covering and stabilizing the lyophobic particles, thus preventing coagulation. This powerfully explains how the stability of lyophobic sols depends on these interactions.

Colloidal stability

Colloidal stability is a crucial factor for colloid survival. It refers to the ability of a colloid particle to remain suspended in its medium without aggregating or settling.

Several factors influence colloidal stability:

• Particle Size: Smaller particles tend to remain suspended longer due to their lower settling rates.
• Concentration of Electrolytes: Electrolytes can either stabilize or destabilize a colloid depending on their concentration.
• Sol Type: Whether a sol is lyophilic or lyophobic greatly affects its stability. Lyophilic sols inherently have greater stability due to their affinity with the solvent.

The key process for stabilizing lyophobic sols involves adding lyophilic sols, which cover and protect lyophobic particles, thus preventing their aggregation and helping them remain dispersed.

In essence, the interaction between lyophilic and lyophobic sols underscores the importance of colloidal stability in various processes, especially in industrial and pharmaceutical applications.